Azeotropic distillation process



United States Patent 3,114,679 AZEOTROPIC DISTILLATION PROCESS Art C. McKinnis, North Long Beach, and Duane L. Flint,

Fullerton, Califi, assignors to Union ()il Company of California, Los Angeles, Calif., a corporation of California Filed Sept. 1, 1961, Ser. No. 135,624 15 Claims. (Cl. 202-42) This invention relates to the recovery of naphthalenic hydrocarbons from mixtures comprising the same, and in particular concerns a method of treating hydrocarbon mixtures boiling within the 390S20 F. range and containing naphthalene and/or alkyl-substituted naphthalenes for the purpose of recovering said naphthalenic hydrocarbons in concentrated form.

The expanding use of naphthalene and alkyl-naphthalenes for the production of di-carboxylic acids useful in manufacturing synthetic resins and fibers has created considerable interest in the recovery of these naphthalenic hydrocarbons from hydrocarbon fractions of petroleum origin. It is well known that certain fractions obtained from certain petroleum refining operations, e.g., catalytic cracking and reforming, contain considerable quantities of naphthalene and alkyl-naphthalenes. However, such fractions also contain large quantities of other hydrocarbon types which have boiling points very close to those of the aforesaid naphthalenic hydrocarbons or which form azeotropes therewith. In either case, satisfactory separation of the naphthalenic from the nonnaphthalenic hydrocarbons cannot be accomplished by fractional distillation. Other conventional separation techniques, e.g., fractional crystallization, solvent extraction, selective complexing, etc., are equally unsatisfactory for use on a commercial scale.

Accordingly, the principal object of the present invention is the provision of an improved method for treating hydrocarbon mixtures boiling within a 390- 520" F. range and comprising naphthalene and/ or alkylnaphthalenes to separate said naphthalenic materials from non-naphthalenic hydrocarbons present in the mixture. A more particular object of the invention is to provide a method whereby non-naphthalenic hydrocarbons boiling in the naphthalene range, that is, within the range of about 400450 F., can be readily separated from mixtures of such hydrocarbons with naphthalene. Other and related objects will become apparent to those skilled in the art as the description of the invention proceeds.

We have discovered that the above objects and attendant advantages can be realized in an azeotropic disstillation process in which maleic anhydride is employed as the azeotrope former. More particularly, we have found that maleic anhydride forms azeotropes of unusually loW boiling point with non-naphthalenic hydrocarbons boiling within the 390-520 F. range, so that by admixing maleic anhydride with a mixture comprising naphthalenic and non-naphthalenic hydrocarbons boiling within said range, and subjecting the resulting mixture to distillation, an exceptionally efficient separation of the two types of hydrocarbons can be achieved. The nonnaphthalenic hydrocarbons distill overhead in the form of low-boiling azeotropes with the maleic anhydride, leaving the naphthalenic material behind as distillation bottoms. The azeotropic distillate is rich in hydrocarbons and has a relatively low heat of vaporization, so that the amount of heat required to separate a unit volume of non-naphthalenic hydrocarbons from the feed mixture is relatively low. Also, maleic anhydride is but slightly miscible with aromatic hydrocarbons, so that in many instances substantially complete separation of the azeotrope-former from the distillate can be achieved by simple gravity settling. Following removal of nonnaphthalenic hydrocarbons, the naphthalene contained in the remaining bottoms fraction can be easily recovered by non-azeotropic distillation, or by any other desired means.

Considering now the process of our invention in greater detail, the feedstock entering said process may be any mixture of hydrocarbons comprising naphthalene and/or alkyl-naphthalenes and at least one non-naphthalenic hydrocarbon which cannot be separated from the naphthalenic components by simple fractional distillation. The term naphthalenic hydrocarbon is herein employed to designate a hydrocarbon compound whose molecule contains the characteristic naphthalene groupmg:

Conversely, the term non-naphthalenic hydrocarbon designates a hydrocarbon compound whose molecule does not contain said grouping. Thus, the non-naphthalenic hydrocarbons which may be present in the feedstock include aliphatic compounds such as dodecane, tetradecane, pentadecane, dodecene, tetradecadiene, etc.; naphthenic compounds such as cyclohexylheptene, hexylcyclohexane, dicyclohexyl, etc.; benzenoid compounds such as triethylbenzene, dimethyl-propylbenzene, diphenyl, phenyl-xylene, octylbenzene, dimethyl-indane, ethyl-indene, etc.; and partially hydrogenated naphthalenic hydrocarbons such as methyl-tetralin, dimethyl tetralin, dihydronaphthalene, methyl-dihydronaphthalene, methyl-decalin, etc. The naphthalenic hydrocarbons which may be present in the feedstock include naphthalene, the methyl-naphthalenes, the dimethylnaphthalenes, the ethyl-naphthalenes, the isopropylnaphthalenes, etc.

While the hydrocarbon feedstocks to the process of our invention can contain any or all of the abovenamed compounds, the process is particularly applicable for the treatment of hydrocarbon mixtures containing naphthalene and contaminated mainly with aromatic hydrocarbons such as alkyl benzenes, alkyl tetralins, alkyl indanes, and the like, boiling within the naphthalene range and thereabouts, e.g., from about 400 to about 450 F. It is known that naphthalene fractions con taining like-boiling parafiin hydrocarbons can be purified by azeotropic distillation with various azeotroping agents. However, a more diflicult problem of separation is in volved in mixtures such as those just named contaminated mainly with aromatic hydrocarbons. Petroleum fractions of this nature can be derived from various hydrocarbon conversion and refining processes commonly used in the industry, such as for example, catalytic reforming, catalytic cracking, thermal cracking and the like. In particular, catalytic reforming of naphthas produces a heavy reformate fraction boiling above about 400 R, which may contain from about 40 to about 80% naphthalene and methyl naphthalenes. The remaining hydrocarbons in this fraction are largely alkyl benzenes, tetralins, indanes, and the like. Sometimes a significant proportion of naphthenes are present, but usually few, if any, paraffins. The recovery of substantially pure naphthalene from such petroleum fractions presents a difficult problem.

Attempts have been made in the past to recover pure naphthalene from such fractions by first subjecting them to catalytic hydrodealkylation to convert the methyl naphthalenes to naphthalene, and then recovering the naphthalene by fractional distillation. None of these methods have proven entirely satisfactory. In fractional crystallization, eutectics are formed which place severe limitations upon the yields of pure naphthalene which can be recovered. Solvent extraction is difficult and expensive where the contaminants are also mainly aromatic in character. Simple fractional distillation is also impractical because of the close proximity of boiling points of the contaminating hydrocarbons, and also the formation of complex azeotropes. These major diffieulties are readily avoided by use of the process. of this in vention.

The feedstocks suitable for treatment as taught herein are not limited to those of conventional petroleum refining origin and may be from any source such as, for example, from destructive distillation or hydrogenation of coal processes or shale oil processes. Usually, however, the feedstock will be of petroleum origin. While the feedstock may be one boiling over the entire 390- 520 F. range, it will usually be one boiling over only a selected portion of such range (e.g., the 400450 F. fraction described above or a fraction boiling at 450- 470 F. and comprising monomethyl naphthalenes, etc.) and may of course contain some components boiling somewhat below or (less desirably) above said range. The feedstock may also be one which has been pretreated to remove part of the naphthalenic components, e.g., it may be a dealkylated petroleum hydrocarbon reformate fraction from which at least part of the naphthalene has been previously separated by crystallization.

Our invention has particular utility for the treatment of hydrocarbon fractions of the aforesaid types containing naphthalene fractions comprising naphthalene and non-naphthalenic hydrocarbon material bOllll'lg within about F. thereof, and especially petroleum fractions within the above category in which the naphthalene fractions boils over the entire range from about 410 to about 450 F. and comprises one or more of the alkyl benzenes, alkyl tetralins and alkyl indanes as the nonnaphthalenic hydrocarbon material. More specifically, petroleum fractions within the above class Wl'llCh. have been found particularly amenable to treatment by the method of this invention are those boiling above about 400 F. which include, as non-naphthalenic hydrocarbons, alkyl benzenes, alkyl tetralins and alkyl indanes boiling over the range from about 410 to about 435 F.; heavy naphtha reformates boiling above about 400 F. and including a naphthalene fraction boiling over the range from about 410 to about 450 F. which preferably contains alkyl benzenes, alkyl tetralins and alkyl indanes; and heavy naphtha reformates which have been subjected to catalytic hydrodealkylation, boiling above about 400 F. and including a naphthalene fraction boiling over the range from about 410 to about 450 F., which naphthalene fraction preferably contains alkyl benzenes, alkyl tetralins and alkyl indanes.

Procedure-wise, our process is carried out as a conventional azeotropic distillation operation, and any of the techniques commonly applied to such types of operation are applicable to the present process. In its simplest embodiment, i.e., batch distillation, the process consists essentially of adding to the feedstock sufficient maleic anhydride to form azeotropes with the non-naphthalenic components, and thereafter distilling the mixture in a reasonably efficient distillation column. The azeotropic distillate is condensed and passed to a separator where the condensate is allowed to separate by gravity into two phases, one of which comprises the non-naphthalenic components of the feedstock containing a small quantity of maleic anhydride and the other of which comprises maleic anhydride containing a relatively small quantity of dissolved non-naphthalenic hydrocarbons. Either or both of said phases may be redistilled or otherwise treated to recover the azeotrope former for reuse. The naphthalenic components of the feedstock are contained in the bottoms fraction which constitutes the desired end product of the process.

In practicing the process of our invention on those naphthalene-aromatic hydrocarbon feedstock mixtures for the separation of which it is most applicable, we have found that substantially all of the alkyl benzenes, alkyl tetralins, and alkyl indanes which boil within about 30 F. of naphthalene can be efiiciently azeotroped overhead before any substantial amounts of naphthalene appear in the overhead product. Moreover, it is found that the azeotropic overhead is unexpectedly rich in hydrocarbons, containing only about 10 to about 60% by weight of maleic anhydride, thus minimizing the distillation load, and the amount of azeotroping agent required. It should be cautioned, however, that since maleic anhydride, as those skilled in the art appreciate, is somewhat lachrymatory, reasonable precautions should be taken to prevent undue pollution of the air in the vicinity of its use. Precautions should also be taken to prevent the contact of maleic anhydride with caustic or other alkali compounds or amines to obviate any possibility of a run-away exothermic decomposition of the maleic anhydride as a result of catalytic influence by the caustic or equivalent.

Attention is now directed to the accompanying drawing, which illustrates schematically one method of practicing the azeotropic distillation process of this invention. The initial feedstock is brought in through line 2 and admitted to distillation column 4 wherein the primary azeotropic distillation takes place. Column 4 may be a conventional fractional distillation column containing, for example, 20-80 plates and may be operated at overhead reflux ratios of, e.g., 1:1 to 20:1. Azeotroping is continued until essentially all of the non-naphthalenic hydrocarbons boiling within about 10 F., and preferably 20 F., of naphthalene are distilled overhead. The overhead temperatures during azeotropic distillation will usually range between about 370 and about 395 F., maleic anhydride itself boiling at about 396 F. The azeotropic overhead is taken off through line 6 and condensed in condenser S, and the resulting condensate is transferred by line 10 to a liquid phase separator 12. To provide the desired refiux ratio, a portion of the condensate in line 10 may be diverted through line 16 and admitted to the top of column 4.

In phase separator 12, the condensate may separate spontaneously into two phases, or a small proportion of a miscibility reducing agent may be required, depending upon the nature of the feed. If the feed is rich in lower alkylated aromatics a miscibility reducing agent is ordinarily required, but if it is rich in higher alkylated aromatics and/ or in naphthenes, adequate phase separation occurs spontaneously. Suitable miscibility reducing agents include anti-solvents for maleic anhydride, e.g., parafiinic or naphthenic hydrocarbons such as pentane, decane, cyclohexane or the like. Preferably, the miscibility reducing agent should be easily separable, as by distillation, from the phase in which it is dissolved.

The solvent rich phase which stratifies in separator 12 will ordinarily contain about 1 to about 25% by weight of dissolved hydrocarbons, and this solution is continuously recycled via line 14 back to a mid-point in distillation column 4.

The hydrocarbon rich phase in separator 12 ordinarily will contain about 1 to about 15% by weight of dissolved maleic anhydride. This hydrocarbon rich phase is then transferred via line 18 to fractionating column 20, from which the maleic anhydride is distilled overhead via line 22 as an azeotrope with a portion of the non-naphthalenic hydrocarbons, and condensed into separator 12. The non-naphthalenic hydrocarbons are withdrawn as bottoms from column via line 24.

A napthalene-containing bottoms fraction is continuously withdrawn from azeotroping column 4- v-ia line 26, and transferred to naphthalene fractionating column 28. Since substantially all of the close-boiling non-napthalenic hydrocarbons have been removed in column 4, the principal separation which is achieved in column 28 is normally the separation of naphthalene from alkyl naphthalenes such as for example, methyl naphthalenes. The naphthalene overhead is withdrawn via line 30 and condensed in cooler 32 to substantially pure naphthalene crystals melting at about 80 C. These crystals are normally in excess of 99% pure. The alkyl naphthalene The 400-500+ F. fraction of a reformate product was separated therefrom by distillation and subjected to a hydrocarbon type anaylsis. The results of the analysis are set forth below.

The distribution of the naphthalenes was found to be as follows (the figures representing weight percentages of the total sample) CmHs 8.7 C11H10 21.0 Ciel-I12 6.4 cisH'it a 1.3 CmHm 0.3 CIGIIIE 0.1

The 400-550+ F. reformate fraction was subjected to batch distillation in a 30-plate Oldershaw column at a 10:1 reflux ratio and in the absence of an azeotroping bottoms from column 28 is withdrawn via line 34 and agent. The fractions obtained from the batch distillamay be sent to dealkylation facllities not shown on the 25 tion were analyzed for hydrocarbon types. Results of drawing to produce additional naphthalene. Such dethese analyses appear in Table 1 below:

Table 1 Boiling Point,I". ,400420420-430 43(1435 435 140 440 145 445 1501450455 455 100450-455 405-470 470-540 540-550 Weight pereent- 18. 5 18.3 5. 07 7.14 5. 05 3. 38 2. 04 2. 44 4. 22 13. 3 14. 4a 0.

Alkangs 11.0 9.8 9.1 8.7 8.1 7.2 3.5 2.7 0.7

Mono-naphthenes 4.1 4. 4 4. 3 4. 5 4. 0 3. 3 4. 6 2.1 1. 4 0. 6

1 naphthenes 1. 9 2. 2 2. 7 2. 0 2. a 3.1 2. 0 2. a 1. 9 0. 7 0. 5 0. 5

Alkylbenzencs. 34. 5 34.1 34.0 34. 2 32. 2 28.8 20.1 10. 3 10. 9 4. 4 2. 0 3. 9

Tetralinindane 2s. 9 a0. 8 39. 0 38. 9 44.1 48. 5 41.7 30. 4 20. s 9. 1 4. s 1. 5

Naphthalenes. 18.5 10. 2 10. s 11. 0 8. 8 9.1 27.1 39. 7 58.3 85.1 80. 6 53. 2

alkylation facilities may consist of any conventional catalytic hydrodealkylation process. An especially preferred technique for dealkylating methyl napththalenes employs steam and hydrogen at elevated temperatures and pressures over a cobalt molybdate catalyst, as is more particularly described in U.S. Patent No. 2,734,929 to Doumani. Where the column 28 bottoms product is subjected to dealkylation, the resulting dealkylate can be recycled to admixture with the feed to column 4 if desired.

The foregoing is not to be considered limitative of the scope of the process. As those skilled in the art will understand, other conventional azeotropic techniques may be employed, and other conventional methods such as fractional crystallization may be employed to recover naphthalene from the azeotroping bottoms.

While maleic anhydride also forms an azeotrope with naphthalene, no difliculty is experienced in obtaining adequate fractionation in column 4 since there is a substantial boiling point difference between that azeotrope and those distilled overhead in that column. If desired, column 28 can also be operated as an azeotropic distillation with maleic anhydride, in which case a less efiicient col umn is required since the naphthalene-maleic anhydride azeotrope boils lower than naphthalene itself.

The effectiveness of our process is more particularly illustrated by the following examples. These examples are, however, not to be construed as limitative, but merely exemplary of the invention.

EXAMPLE I This example is included to illustrate the inefiicacy of straight distillation as a means of separating naphthalenic from non-naphthalenic hydrocarbons in admixture therewith.

In evaluating the Table 1 data, it will be noted that the bulk of all components of the feedstock except the higher boiling alkylnaphthalenes distilled off in the fractions within the boiling point range from 400 to 450 F. It will be further noted that none of the six fractions within that range show any practically significant enrichment in either naphthalene or non-naphthalenic hydrocarbons over the starting material.

Turning next to the higher boiling fractions, particular- 1y those between 450 and 540 F., it will be observed that no practical selectivity was effected there either. Thus, while the bulk of the alkylnaphthalene portion of the feed distilled within that range there was also much alkylbenzene and tetralin-indane distillation to mitigate against economically acceptable selectivity of separation therein. This was particularly true of the boiling point range from 450 to 465 F.

EXAMPLE II This is an example of a continuous azeotropic distillation of a reformate fraction boiling between 400 and 445 F., using maleic anhydride as the azeotrope former. The reformate fraction contained 43 weight percent naphthalene and 1 weight percent methylnaphthalene, the remainder being alkanes, naphthenes, alkylbenzenes, tetralins and indanes. The maleic anhydride was employed in a ratio of 74 volumes per volumes of reformate feed. The distillation column employed was a conventional vacuum jacketed glass Oldershaw column with 60 perforated plates of 28 mm. 1.1)., each having 82 holes of 0.89 mm. diameter. The plate to plate spacing was approximately 27 mm. The distillation was conducted at a reflux ratio of 8.421.

In carrying out the continuous distillation operation angers of this example, the reformate feedstock was continuously introduced into the 60-plate Oldershaw column along with a properly proportioned volume of maleic anhydride. The column was operated to produce an overhead vapor stream at a temperature of about 381 F. and a bottoms fraction boiling above about 424 F. The latter fraction was continuously withdrawn from the bottom of the Oldershaw column as the process product, and comprised about 90 percent by weight naphthalene.

The overhead from the column was condensed and separated into two phases-a hydrocarbon phase comprising primarily non-naphthalenic components of the feedstock, but including 6 percent by weight maleic anhydride, and a maleic anhydride phase.

The bottoms product from the azeotropic distillation was subjected to straight batch distillation in a 30-plate Oldershaw column at a reflux ratio of 15:1. The overhead product -was a phthalic grade naphthalene of 79 C. melting point. The overall recovery of naphthalene was 77 percent. This figure is actually somewhat on the low side due to some difiiculty encountered in setting the proper cut point in the continuous distillation run and to somewhat excessive loss of naphthalene in the batch distillation bottoms, both of which occurrences are read- =ily curable by a tightening of the controls on the two operations involved.

The results of this example clearly illustrate the excellent selectivity attainable through the use of maleic anhydride as an azeotrope former in the method of our invention. They also illustrate that such selectivity is not dependent upon the use of large quantities of maleic anhydride but, on the contrary, that relatively small quantities are suflicient for the purpose. Thus, in the present example the ratio of maleic anhydride to nonnaphthalene feedstock hydrocarbons, on a volume basis, was only 1.2 to one.

EXAMPLE HI This example is illustrative of the separation of nonnaphthalene hydrocarbons from alkyl naphthalenes according to the method of this invention.

A bottoms fraction of a platinum-catalyzed reformer product having a boiling range of 385440 F. is hydrodealkylated over a cobalt oxide-molybdenum oxide catalyst to produce a dealkylated product boiling over the range =l4l550 F. This product is fractionally distilled to obtain a light gasoline fraction boiling at 141 401 F., a naphthalene fraction boiling at 401438 F, a methyl-naphthalene fraction boiling at 456467 R,

' and a heavy fraction boiling at 493 -550 F. Analysis shows the methylnaphthalene fraction to contain about 90.5 percent weight of 1- and Z-methylnaphthalenes and about 9.5 percent by weight of non-naphthalenic hydrocarbons, presumably alkyltetralins and alkylindanes. This material, together with 40 percent by weight of maleic anhydride, is introduced into a 6Q-plate Oldershaw column and a distillation is carried out therein to yield a bottoms product enriched in methylnaphthalenes.

It will be apparent that the method of our invention is applicable for use in the separation of many hydrocarbon mixtures other than those described in the above examples. Thus, any hydrocarbon mixture within the purview of this invention can be separated into nonnaphthalenic and naphthalenic fractions by azeotropically distilling it in the presence of maleic arihydride in accordance with the teachings herein.

We claim:

1. A process for the separation of naphthalene from a hydrocarbon mixture boiling within the range from about 390 F. to about 520 F., and comprising naphthalenic and non-naphthalenic components which are not separable by simple fractional distillation which comprises azeotropically distilling said mixture together with maleic anhydride to vaporize said non-naphthalenic components together with said maleic anhydride as a minio 0 mum boiling azeotropic distillate, thereby leaving as azeotropic bottoms a product in which the ratio of naphthalenic to non-naphthalenic hydrocarbons is substantially greater than the ratio thereof in said hydrocarbon mixture.

2. A process as defined by claim 1 wherein the naphthalenic components of said hydrocarbon mixture include naphthalene and methylnaphthalenes.

3. A process as defined by claim 1 wherein the nonnaphthalenic components of said hydrocarbon mixture include at least one hydrocarbon type from the class consisting of alkyl benzenes, alkyl tetralins and alkyl indanes.

4. A process as defined by claim 1 wherein said hydrocarbon mixture is one obtained by fractionally distilling a product obtained by the catalytic dealkylation of a platinum-catalyzed reformate fraction boiling between about 385 F. and about 440 F.

5. A process for the separation of naphthalene from a hydrocarbon mixture boiling within the range from about 390 F. to about 520 F., and comprising naphthalenic and non-naphthalenic hydrocarbons which are not readily separable by simple fractional distillation means, comprising: (11) introducing said hydrocarbon mixture into a distillation column together with sufficient added maleic anhydride to vaporize substantially all of said non-naphthalenic hydrocarbons together with substantially all of said maleic anhydride as a minimum boiling azeotropic distillate; (2) withdrawing said distillate from said column as an overhead stream; (3) condensing said distillate and allowing the azeotropic condensate to separate into two liquid phases, one phase comprising maleic anhydride and a minor proportion of non-naphthalenic hydrocarbons and the other phase comprising non-naphthalenic hydrocarbons and a minor proportion of maleic anhydride; (4) returning the phase comprising maleic anhydride and a minor proportion of non-naphthalenic hydrocarbons to said distillation column; (5) fractionally distilling the phase comprising non-naphthalenic hydrocarbons and a minor proportion of maleic anhydride to obtain an overhead azeotropic distillate of maleic anhydride and non-naphthalenic hydrocarbons and a bottoms product comprising non-naphthalenic hydrocarbons; (6) combining the overhead azeotropic distillate from step (5) with the azeotropic distillate from step (1) prior to condensation and phase separation thereof; (7) and withdrawing from said distillation column a bottoms product in which the ratio of naphthalenic to non-naphthalenic hydrocarbons is substantially greater than the ratio thereof in said hydrocarbon mixture.

6. A process as defined by claim 5 wherein the naphthalenic fraction of said hydrocarbon mixture includes naphthalene and methylnaphthalenes.

7. A process as defined by claim 5 wherein the nonnaphthalenic fraction of said hydrocarbon mixture includes at least one hydrocarbon type from the class consisting of alkyl benzenes, alkyl tetralins and alkyl indanes.

8. A method for the recovery of substantially pure naphthalene from a petroleum fraction comprising naphthalenic and non-naphthalenic hydrocarbon components not readily separable by simple fractional distillation, boiling above about 400 R, which comprises: (1) subjecting said fraction to azeotropic distillation in admixture with maleic anhydride until a major proportion of the nonnaphthalenic hydrocarbons in said fraction which boil within about 10 Fahrenheit degrees of naphthalene is distilled overhead with maleic anhydride as an azeotropic distillate; and (2) recovering substantially pure naphthalene from the remaining bottoms fraction.

9. The method of claim 8 in which said non-naphthalenic hydrocarbon components comprise at least one hydrocarbon type from the class consisting of alkyl benzenes, alkyl tetralins and alkyl indanes.

10. The method of claim 8 in which said non-naphthalenic hydrocarbon components include alkyl benzenes,

9 alkyl tetralins and alkyl indanes boiling Within the range from about 410 F. to about 435 F.

11. The method of claim 8 in which said petroleum fraction is a heavy naphtha reformate including a naphthalene fraction boiling over the range from about 410 F. to about 450 F.

12. The method of claim 8 in which said petroleum fraction is a heavy naphtha reformate which has been subjected to catalytic hydrodealkylation, and which includes a naphthalene fraction boiling within the range from about 410 F. to about 450 F.

13. A method for the recovery of substantially pure naphthalene from a petroleum distillate comprising a naphthalene fraction boiling within the range from about 410 F. to about 450 F., said naphthalene fraction also containing alkyl benzenes, alkyl tetralins and alkyl indanes, which comprises: (1) subjecting said naphthalene fraction to azeotropic distillation in admixture with maleic anhydride until substantially all of the non-naphthalenic hydrocarbons in said fraction which boil within about 20 Fahrenheit degrees of naphthalene are distilled overhead as an azeotropic distillate with said maleic anhydride; and (2) distilling the remaining bottoms fraction in the absence of maleic anhydride to recover substantially pure naphthalene as an overhead product.

14. The method of claim 13 in which said petroleum distillate is a heavy naphtha reformate boiling above about 400 F.

15. The method of claim 13 in which said petroleum distillate is a heavy naphtha reformate which has been subjected to catalytic hydrodealkylation, and which boils above about 400 F.

References Cited in the file of this patent UNITED STATES PATENTS 2,551,912 Teter May 8, 1951 2,734,929 Doumani Feb. 14, 1956 2,945,902 Romans July 19, 1960 3,043,890 McKinnis July 10, 1962 

1. A PROCESS FOR THE SEPARATION OF NAPHTHALENE FROM A HYDROCARBON MIXTURE BOILING WITHIN THE RANGE FROM ABOUT 390*F. TO ABOUT 520*F., AND COMPRISING NAPHTHALENIC AND NON-NAPTHTALENIC COMPONENTS WHICH ARE NOT SEPARABLE BY SIMPLE FRACTIONAL DISTILLATION WHICH COMPRISES AZEOTROPICALLY DISTILLING SAID MIXTURE TOGETHER WITH MALEIC ANHYDRIDE TO VAPORIZE SAID NON-NAPHTHALENIC COMPONENTS TOGETHER WITH SAID MALEIC ANHYDRIDE AS A MINIMUM BOILING AZETROPIC DISTILLATE, THEREBY LEAVING AS AZEOTROPIC BOTTOMS A PRODUCT IN WHICH THE RATIO OF NAPHTHALENIC TO NON-NAPHTHALENIC HYDROCARBONS IS SUBSTNTIALLY GREATER THAN THE RATIO THEREOF IN SAID HYDROCARBON MIXTURE. 